Suggestions for determining my distance gaps?

Ive been going to my local range and have gotten a rough idea of what the shorter half of my club distances are. Trouble is, the lie off the tee box at the range is nothing like my usual lie on the course, and I'm starting to feel like the yardage markers on this range aren't really that accurate. Not to mention, guessing carry distance is undoubtedly highly inaccurate.

I don't really have a good place around my residence to take a bag of shag balls and hack it out, so I was thinking of purchasing a GPS that I could record and analyze distances over time as I play on the course. Any suggestions for a good device to do this with?

Any other ideas on how to work on getting an accurate idea of my distance gaps?

I've got mine based on trial and error. Although, if I see a guy at the range using a laser to sight the targets, I will bug him for a few numbers. There is not only the aspect you mentioned of the quality of the turf, but also the quality (and type) of the balls at the range.

I would suggest doing your best to get an estimate of your 8-iron, maybe, and just figure roughly 10 yards either way from that for each iron up and down. Then over time on the course, you'll eventually figure it out.

Hit ball, check distance, rinse and repeat.......many, many times. As has been said, estimate your gaps at 10 yards or so and go from there. Unfortunately, there's just no substitute for repetition....

I have one of the Garmin GPS watches. You can use it to specifically measure a shot, but for me it has been more useful in just getting a feel for how far you generally hit various clubs. I have found that, though you can start this process on the range, you are much better off learning the fineness of this on the course with your game ball.

Range balls generally do not perform like the balls you are likely to actually play. That doesn't mean practicing with them is useless by any means, but lasering your distances with them may not really translate to the course.

Distance control is, I believe, the strongest argument for picking out a ball within a price point you are comfortable with and sticking to it rather than just playing whatever was on sale last time you needed to buy balls.